PROJECT SUMMARY Alcohol consumption has been linked to increased risk of colorectal cancer (CRC). However, the underlying mechanisms have not yet been fully defined. Emerging evidence from animal studies suggest that alcohol associated gut dysbiosis and subsequent gut barrier dysfunctions and endotoxemia may be an important and underexplored pathway. However, the impact of long-term alcohol intake on not only the taxonomic makeup but also the functional capacity of the gut microbiome among healthy individuals has not been established, and how these dysbiosis will influence colorectal carcinogenesis remain unknown. Alcohol-associated passage of luminal endotoxin into systemic circulation is hypothesized to activate both adaptive and innate immune systems characterized by a release of antibodies, cytokines, and other inflammatory mediators, which may increase subsequent risk of inflammation related diseases, including obesity, and diabetes, both of which are well-established risk factors for CRC. However, the role of endotoxemia in colorectal carcinogenesis has not been studied. We therefore hypothesize that long-term alcohol intake induce gut dysbiosis, impair the gut barrier function, and followed by endotoxemia and inflammation to increase risk of CRC. We will test this hypothesis leveraging rich data collected a large and well-characterized prospective cohort (the Health Professional Follow-up Study) with a healthy sub-cohort with stool collection and metagenomic and metatranscriptomic profiling (Aim 1a) and 250 nested CRC cases and 250 controls with archived pre- diagnostic blood and ongoing plasma proteomic profiling (Aim 1b and 1c). Specifically, we will investigate whether long-term alcohol intake induce gut dysbiosis through perturbations in microbial composition (e.g. Proteobacteria) and function of tumor-permissive immune signatures and procarcinogenic pathways among healthy individuals (Aim 1a). We will also investigate whether alcohol-associated colorectal carcinogenesis is mediated by gut barrier dysfunction and endotoxemia through first identifying circulating markers of gut wall integrity loss, bacteria translocation, endotoxemia, inflammation associated with alcohol intake (Aim 1b), and then investigate their associations with subsequent risk of CRC (Aim 1c). Our findings will provide novel mechanistic insight into gut microbial and endotoxemia mediated pathogenesis of alcohol-related CRCs. We will also provide clinically translatable data including specific microbial targets, and circulating biomarkers and network that reflect susceptibilities to subsequent risk of alcohol-related CRCs.